JP7480397B2 - Quaternary alkyl ammonium hypochlorite solution - Google Patents

Description

The present invention relates to a quaternary alkyl ammonium hypochlorite solution and a method for producing the same. More specifically, the present invention relates to a quaternary alkyl ammonium hypochlorite solution with excellent storage stability and a method for producing the same. The present invention also relates to a quaternary alkyl ammonium hypochlorite solution with reduced metal impurities that is suitable for cleaning semiconductor wafers and elements, and a method for producing the same.

In recent years, design rules for semiconductor elements have become increasingly finer, leading to stricter requirements for impurity management in the semiconductor element manufacturing process. Because the impurities generated in the semiconductor element manufacturing process differ for each manufacturing process, it is important to identify the source of contamination for each manufacturing process and to manage the concentration of the impurities that are the source of contamination.

In addition, large-diameter semiconductor wafers exceeding 300 mm are being used to improve the manufacturing efficiency of semiconductor elements. In large-diameter semiconductor wafers, the area of the end faces and back faces where electronic devices are not fabricated is larger than that of small-diameter semiconductor wafers. Therefore, in the process of forming metal wiring and the process of forming barrier metal, metal wiring material and barrier metal material (hereinafter sometimes collectively referred to as "metal materials, etc.") are likely to adhere not only to the surface of the semiconductor wafer where the semiconductor elements are formed, but also to the end faces and back faces. As a result, the amount of excess metal materials, etc. adhering to the end faces and back faces of large-diameter semiconductor wafers is greater than that of small-diameter wafers.

Excess metal materials adhering to the edge or back surface of semiconductor wafers can contaminate the manufacturing equipment as metal or metal oxide particles during the oxygen ashing process or plasma dry etching process, which are processes that follow the formation of metal wiring and barrier metal, and can cause cross-contamination. For this reason, metal materials adhering to the edge or back surface needed to be removed before being brought into the next process.

Among these metal materials, precious metals such as platinum and ruthenium are difficult to oxidize, dissolve, and remove in the subsequent etching and cleaning processes. For this reason, it is preferable to remove these precious metals from the semiconductor wafer in preference to other metal materials. Ruthenium in particular is widely used as a wiring material for semiconductor device design rules of 10 nm or less because it can reduce resistance more than copper is used as a wiring material, and it is therefore desirable to remove it quickly from unnecessary areas.

Generally, a cleaning method using hypochlorite, which has a high oxidizing power, has been proposed as a cleaning solution for semiconductor wafers. Specifically, a method using an aqueous solution of sodium hypochlorite has been proposed (see Patent Documents 1 and 2).

However, when using an aqueous solution of sodium hypochlorite as a cleaning solution, the cleaning solution inevitably contains a large amount of sodium ions. As a result, sodium ions tend to adhere to semiconductor wafers and the like, which may reduce the efficiency of semiconductor production.

In response to this, development has also been carried out of cleaning solutions that use hypochlorous acid solutions that do not contain sodium as an essential component (see Patent Document 3) or aqueous solutions of quaternary alkyl ammonium hypochlorite (see Patent Document 4).

However, these cleaning solutions using hypochlorous acid (see Patent Document 3) are used to clean substrates with metal or metal oxide films, and are not specifically intended to remove precious metals. Therefore, they are not suitable for cleaning metal/metal oxide films such as precious metals.

On the other hand, the cleaning solution containing the tetramethylammonium hypochlorite aqueous solution described in Patent Document 4 is also a cleaning solution used to clean photoresist and residues, and is not intended to clean metal coatings such as copper and aluminum containing ruthenium. Specifically, the examples show that the metal film is difficult to etch.

JP 2002-161381 A JP 2009-081247 A JP 2003-119494 A JP 2005-227749 A

The storage stability of the tetramethylammonium hydroxide solution in Patent Document 4 is not necessarily satisfactory. In other words, the inventors' investigations have revealed that the desired cleaning performance is not achieved due to the decrease over time of hypochlorite ions, which exert an oxidizing effect.

Patent document 4 also discloses that, for example, triazoles, thiazoles, tetrazoles and imidazoles are added to the cleaning composition as stabilizers to maintain the level of available halogens.

However, the addition of stabilizers tends to leave organic residue after cleaning, which can lead to reduced yields of semiconductor devices. Stabilizers also tend to adsorb to certain metals, such as triazole, copper, which can reduce their ability to clean copper.

Therefore, the first object of the present invention is to provide a method for producing a quaternary alkylammonium hypochlorite solution that exhibits little change in hypochlorite ion concentration over time and has excellent storage stability even without the addition of a stabilizer.

The cleaning solution containing the tetramethylammonium hypochlorite aqueous solution described in Patent Document 4 is intended to remove photoresist residues, as described above. For this reason, no consideration is given to reducing the metal content of, for example, sodium, aluminum, and/or potassium in the cleaning solution. It is believed that a cleaning solution with a lower metal content can improve the production efficiency of semiconductor elements.

Therefore, the second object of the present invention is to provide a quaternary alkyl ammonium hypochlorite solution with a reduced metal content for use in the process of manufacturing semiconductor devices, and a method for producing the same.

The present inventors have conducted extensive research to achieve the first objective. They have discovered that because the pH of the quaternary alkyl ammonium hypochlorite solution is not controlled during the reaction, the concentration of hypochlorite ions present in the quaternary alkyl ammonium hypochlorite solution decreases, resulting in a decrease in cleaning and removing power.

In other words, the concentration of hypochlorite ions changes significantly depending on the pH of the quaternary alkyl ammonium hypochlorite solution in the reaction process. As a result of further investigation into the factors that cause the pH to fluctuate in the reaction process, it was found that carbon dioxide in the gas phase of the reaction process is absorbed into the reaction liquid, causing the pH of the reaction liquid to fluctuate significantly, and that by controlling the carbon dioxide concentration in the gas phase of the reaction process, a quaternary alkyl ammonium hypochlorite solution with high storage stability can be produced without adding a stabilizer.

Further investigations based on the above findings led to the discovery that the storage stability of a quaternary alkyl ammonium hypochlorite solution, which can be suitably used as an oxidizing agent and cleaning agent, can be further improved by adjusting the pH of the quaternary alkyl ammonium hypochlorite solution without the addition of a stabilizer.

That is, it was found that the reaction rate of the disproportionation reaction of hypochlorous acid and hypochlorite ions varies depending on the pH of the quaternary alkyl ammonium hypochlorite solution, and that there is a pH range in which the self-decomposition of hypochlorous acid and hypochlorite ions is suppressed. In general, it is known that the disproportionation reaction of hypochlorous acid and hypochlorite ions is suppressed in sodium hypochlorite solutions at an alkaline pH, for example, at a pH of 11 or higher, but it was found that the disproportionation reaction of hypochlorous acid and hypochlorite ions is specifically suppressed in quaternary alkyl ammonium hypochlorite solutions at a pH of 12 or higher but lower than 14.

For example, when the quaternary alkyl ammonium hypochlorite solution of the present invention is used for cleaning and removing metals, the optimal pH of the quaternary alkyl ammonium hypochlorite solution is greater than 7 and less than 12. However, the inventors' investigations have revealed that when a quaternary alkyl ammonium hypochlorite solution is prepared and stored within this pH range, it loses a significant amount of oxidizing power in a short period of time.

Based on these findings, we found that by adjusting the pH of a quaternary alkyl ammonium hypochlorite solution, the hypochlorite ion concentration does not decrease and the storage stability of the quaternary alkyl ammonium hypochlorite solution is improved without adding a stabilizer.

The inventors have also conducted extensive research to achieve the second objective. First, they conducted a detailed study of metal impurities that may be contained in the quaternary alkylammonium hypochlorite solution described in Patent Document 4.

In Patent Document 4, the purpose is to remove photoresist, so the need to reduce the metal atoms contained in the aqueous solution of tetramethylammonium hypochlorite is not taken into consideration.

Specifically, in the examples of Patent Document 4, an aqueous solution of tetramethylammonium hypochlorite is produced by reacting an aqueous solution of tetramethylammonium hydroxide with chlorine gas in an Erlenmeyer flask. Since there is no mention of the flask, it is highly likely that it is a glass container. According to the inventors, in a follow-up test of the example, it was found that the resulting quaternary alkylammonium hypochlorite solution contains a relatively large amount of metal atoms such as sodium.

The inventors therefore investigated the cause of the inclusion of metal atoms such as sodium. They concluded that one of the causes was due to the raw material quaternary alkyl ammonium hydroxide and the material of the flask. In other words, they presumed that the cause was that metal atoms such as sodium were dissolved from the glass of the flask, because quaternary alkyl ammonium hydroxide is a substance that exhibits strong alkalinity. They then discovered that the above problem could be solved by limiting the material of the reaction vessel when reacting the aqueous solution of quaternary alkyl ammonium hydroxide with chlorine gas.

That is, the present invention includes the following gist.
(1) A method for producing a quaternary alkyl ammonium hypochlorite solution, comprising the steps of:
The method includes the steps of: preparing a quaternary alkyl ammonium hydroxide solution; and contacting the quaternary alkyl ammonium hydroxide solution with chlorine.
The carbon dioxide concentration in the gas phase in the reaction step is 100 ppm by volume or less, and the pH of the liquid phase in the reaction step is 10.5 or more.
A method for producing a quaternary alkyl ammonium hypochlorite solution.

(2) The method according to (1), in which the quaternary alkyl ammonium hydroxide solution prepared in the preparation step is a solution of quaternary alkyl ammonium hydroxide in which the alkyl group has 1 to 10 carbon atoms.

(3) The method according to (1) or (2), wherein the reaction temperature in the reaction step is -35°C or higher and 15°C or lower.

(4) The method according to any one of (1) to (3), wherein in the reaction step, the carbon dioxide concentration in the quaternary alkyl ammonium hydroxide solution is 500 ppm or less.

(5) A method for producing a quaternary alkyl ammonium hypochlorite solution, comprising a reaction step of contacting a quaternary alkyl ammonium hydroxide solution with chlorine gas in a reaction vessel,
A method for producing a quaternary alkyl ammonium hypochlorite solution, wherein the surface in the reaction vessel that comes into contact with the quaternary alkyl ammonium hydroxide solution is made of an organic polymer material.

(6) The method according to (5), wherein the organic polymer material is a fluororesin.

(7) The method according to (5) or (6), wherein the moisture content of the chlorine gas is 10 ppm by volume or less.

(8) The method according to any one of (1) to (7), further comprising a step of filtering the quaternary alkyl ammonium hypochlorite solution obtained in the reaction step.

(9) The method according to (8), in which the pH of the quaternary alkyl ammonium hypochlorite solution to be filtered at 25°C is 13.5 or less.

(10) The method according to (9), in which the pH of the quaternary alkyl ammonium hypochlorite solution to be filtered at 25°C is 12.5 or less.

(11) The method according to any one of (1) to (10), further comprising a preservation step of preserving the reaction solution after the reaction step, in which the pH of the quaternary alkyl ammonium hypochlorite solution at 25°C is adjusted to 12.0 or more and less than 14.0 during the preservation step.

(12) The method according to (11), which includes a dilution step for adjusting the pH of the reaction solution after the storage step, and in the dilution step, the pH of the quaternary alkyl ammonium hypochlorite solution at 25°C is adjusted to 8.0 or more and less than 12.0.

(13) The method according to (12), wherein the dilution step is a step of diluting the stored quaternary alkyl ammonium hypochlorite solution with a solution having a pH at 25°C of greater than 0 and less than or equal to 7.

(14) A method for treating a semiconductor wafer, comprising treating the surface of the semiconductor wafer with a quaternary alkyl ammonium hypochlorite solution obtained by the method described in any one of (1) to (13) above.

(15) The processing method described in (14), wherein the semiconductor wafer is a semiconductor wafer containing at least one selected from the group consisting of copper, tungsten, tantalum, titanium, cobalt, ruthenium, manganese, aluminum, silicon, silicon oxide, and compounds thereof.

(16) A quaternary alkylammonium hypochlorite solution having a sodium, potassium, and aluminum metal content of less than 1 ppb each.

(17) A quaternary alkyl ammonium hypochlorite solution as described in (16), further comprising less than 1 ppb of each of the metals magnesium, iron, nickel, copper, silver, cadmium, and lead.

(18) A quaternary alkyl ammonium hypochlorite solution according to (16) or (17), having a pH of 9.0 or more and 12.5 or less at 23°C.

According to the first embodiment of the present invention described above in (1) to (4), a quaternary alkyl ammonium hypochlorite solution having high storage stability can be produced without adding a stabilizer such as triazole, thiazole, tetrazole, or imidazole. In addition, the resulting quaternary alkyl ammonium hypochlorite solution does not require the addition of a stabilizer that does not affect the cleaning ability. Therefore, if the quaternary alkyl ammonium hypochlorite solution produced by the present invention is used in the semiconductor manufacturing process, it can be suitably used as a cleaning solution that does not reduce the yield.

According to the second embodiment of the present invention described above in (5) to (7), a quaternary alkyl ammonium hypochlorite solution with a low metal content can be obtained. Therefore, it can be suitably used as an etching solution or cleaning solution when manufacturing semiconductor devices.

In addition, by including the above filtration steps (8) to (10), the metal content in the quaternary alkylammonium hypochlorite solution can be further reduced.
As described above in (11), by controlling the pH during storage, the storage stability can be further improved.
The effects achieved by each embodiment of the present invention will be described in more detail below.

FIG. 1 is a schematic diagram showing one embodiment of a method for producing a quaternary alkyl ammonium hypochlorite solution according to a first embodiment. FIG. 11 is a schematic diagram showing one embodiment of a method for producing a quaternary alkylammonium hypochlorite solution according to a second embodiment. FIG. 1 is a schematic diagram showing one embodiment of a general method for producing a quaternary alkyl ammonium hypochlorite solution.

<First embodiment: Method for producing quaternary alkyl ammonium hypochlorite solution>
The method for producing a quaternary alkyl ammonium hypochlorite solution according to the first embodiment includes a preparation step of preparing a quaternary alkyl ammonium hydroxide solution, and a reaction step of contacting the quaternary alkyl ammonium hydroxide solution with chlorine.
The method is characterized in that the carbon dioxide concentration in the gas phase in the reaction step is 100 ppm by volume or less, and the pH of the liquid phase in the reaction step is 10.5 or more.
Each step will be described below.

(Preparation step of preparing quaternary alkyl ammonium hydroxide solution)
The quaternary alkyl ammonium hydroxide solution may be either an aqueous solution in which the quaternary alkyl ammonium hydroxide is dissolved in water or a solution in which the quaternary alkyl ammonium hydroxide is dissolved in a non-aqueous solvent. The quaternary alkyl ammonium hydroxide solution can be obtained by dissolving the quaternary alkyl ammonium hydroxide in water or a non-aqueous solvent, or by diluting a commercially available quaternary alkyl ammonium hydroxide solution to a desired concentration. Examples of the non-aqueous solvent include known organic solvents that can dissolve the quaternary alkyl ammonium hydroxide. Specifically, alcohol and glycol are included, and methanol and propylene glycol are particularly preferred. Among these solvents, the solvent is preferably water, since it is easily available industrially and a high-purity quaternary alkyl ammonium hydroxide solution can be obtained.

The concentration of the quaternary alkyl ammonium hydroxide solution is not particularly limited, but if the concentration of the quaternary alkyl ammonium hydroxide becomes high, the salt will precipitate and become a solid. Therefore, the concentration of the quaternary alkyl ammonium hydroxide solution is preferably 0.01 to 30% by mass, more preferably 0.05 to 27.5% by mass, and even more preferably 0.1 to 25% by mass.

The prepared quaternary alkyl ammonium hydroxide solution usually contains carbon dioxide derived from the atmosphere. Carbon dioxide is present in the solution as carbonate ions or bicarbonate ions. The carbon dioxide concentration is not particularly limited, but is preferably 0.001 ppm to 500 ppm (by mass) in terms of carbonate ions, more preferably 0.005 ppm to 300 ppm, and even more preferably 0.01 ppm to 100 ppm. By having the carbon dioxide concentration in the quaternary alkyl ammonium hydroxide solution be 0.001 ppm to 500 ppm, the pH change of the resulting quaternary alkyl ammonium hypochlorite solution can be suppressed. As a result, the storage stability of the quaternary alkyl ammonium hypochlorite solution can be improved. A commercially available quaternary alkyl ammonium hydroxide solution having such a carbon dioxide concentration can be used.

The solvent for preparing the quaternary alkyl ammonium hydroxide solution may be an aqueous solution using only water as the solvent, or a non-aqueous solution may be prepared by mixing with an organic solvent. The solvent can be changed appropriately depending on the application of the quaternary alkyl ammonium hypochlorite solution and the object to be cleaned. For example, when the object to be cleaned is ruthenium, water alone is sufficient for cleaning, so an aqueous solution of quaternary alkyl ammonium hydroxide can be prepared.

In this embodiment, the quaternary alkyl ammonium hydroxide solution is preferably a solution of quaternary alkyl ammonium hydroxide in which the alkyl group has 1 to 10 carbon atoms, and more preferably a solution of quaternary alkyl ammonium hydroxide in which the alkyl group has 1 to 5 carbon atoms. Specific examples of quaternary alkyl ammonium hydroxide include tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, and tetrabutyl ammonium hydroxide. These quaternary alkyl ammonium hydroxides may be used alone or in combination of two or more types. In addition, the number of carbon atoms of the four alkyl groups contained in the quaternary alkyl ammonium hydroxide may be the same or different.

In the process of producing a quaternary alkyl ammonium hypochlorite solution by reacting a quaternary alkyl ammonium hydroxide solution with chlorine gas, the pH of the solution containing the quaternary alkyl ammonium hypochlorite solution produced in the reaction vessel decreases. Considering the conditions of the filtration operation described below and the solubility of the quaternary alkyl ammonium hydroxide, in this embodiment, the lower limit of the pH of the quaternary alkyl ammonium hydroxide solution used as the raw material is 10.5 or more, preferably 11.0 or more, more preferably 11.5 or more, and particularly preferably more than 12.0. The upper limit of the pH of the quaternary alkyl ammonium hydroxide solution is determined by the concentration of the quaternary alkyl ammonium hydroxide.

In addition, the quaternary alkyl ammonium hydroxide solution used in this embodiment preferably contains metals, specifically, sodium, potassium, aluminum, magnesium, iron, nickel, copper, silver, cadmium, and lead, each of which is 0.01 ppb or more and 20 ppb or less. Of course, the metal content of the quaternary alkyl ammonium hydroxide solution used may be less than 0.01 ppb, but it is difficult to obtain such a quaternary alkyl ammonium hydroxide solution.

Therefore, by using a quaternary alkyl ammonium hydroxide solution whose metal content satisfies the above range, the solution itself becomes easy to obtain, and the metal impurities can be easily removed and reduced by filtration during and after the production of the quaternary alkyl ammonium hypochlorite solution. The reason why metal impurities can be removed and reduced by filtration is not clear, but it is thought that the presence of a certain amount of metal impurities produces impurity particles having a certain size, rather than colloidal impurities that are difficult to remove by filtration, making them possible to remove by filtration. Therefore, the quaternary alkyl ammonium hydroxide solution used in this embodiment can be used suitably even if it is not an ultra-high purity quaternary alkyl ammonium hydroxide solution, because the solid metal impurities can be removed and reduced by filtration due to the lowering of the pH. To further enhance this effect and further remove and reduce impurities that are alkaline and in the form of ions, the metal contents of sodium, potassium, aluminum, magnesium, iron, nickel, copper, silver, cadmium, and lead contained in the quaternary alkyl ammonium hydroxide solution are preferably 0.01 ppb or more and 5 ppb or less, and even more preferably 0.01 ppb or more and 2 ppb or less.

The above-mentioned quaternary alkyl ammonium hydroxide solutions can be commercially available. In particular, quaternary alkyl ammonium hydroxide solutions that have been highly purified by electrolysis and/or contact with ion exchange resins, etc. and are used as photoresist developers for semiconductor devices, can be preferably used. These commercially available solutions can also be used by diluting them with a solvent that does not contain metal impurities, such as ultrapure water.

(Reaction step of contacting quaternary alkyl ammonium hydroxide solution with chlorine)
By contacting and reacting the quaternary alkyl ammonium hydroxide solution with chlorine, the hydroxide ions of the quaternary alkyl ammonium hydroxide are replaced with hypochlorite ions generated by chlorine, and a quaternary alkyl ammonium hypochlorite solution is produced.

In this embodiment, the chlorine gas used is not particularly limited, and commercially available gases can be used. Among them, high-purity gases such as those used for etching semiconductor materials and as raw materials for semiconductor materials can be used.

Among high purity gases, gases with a particularly low moisture content are preferred, and specifically, gases with a moisture content of 10 ppm by volume or less (by mass) are preferred. The reason for this is unclear, but the following is thought to be the case. For example, when producing a quaternary alkylammonium hypochlorite solution, chlorine gas is usually transported through piping. Therefore, if there is a lot of water, hydrogen chloride is generated and corrodes metal components such as piping and flow meters, and it is thought that corroded metal impurities are easily introduced into the system along with chlorine gas. Therefore, it is preferable to use chlorine gas with a moisture content of 10 ppm by volume or less. Naturally, commercially available chlorine gas can be used as is, or the amount of moisture contained in the chlorine gas can be reduced by contacting it with a drying material or the like just before it is introduced into the reaction system. The lower limit of the moisture content of chlorine gas is not particularly limited, but considering that it is industrially available, it is 0.1 ppm by volume.

In this embodiment, the concentration of carbon dioxide contained in the chlorine gas is not particularly limited, but is preferably 0.001 to 80 ppm by volume, more preferably 0.005 to 50 ppm by volume, and even more preferably 0.01 to 2 ppm by volume. If the carbon dioxide concentration contained in the chlorine gas is in the range of 0.001 to 80 ppm by volume, the pH change of the resulting quaternary alkyl ammonium hypochlorite solution can be suppressed. As a result, the storage stability of the quaternary alkyl ammonium hypochlorite solution can be improved. Chlorine gas with such a carbon dioxide concentration can be commercially available.

In this embodiment, the method of contacting the quaternary alkyl ammonium hydroxide solution with chlorine is not particularly limited, and known methods can be used. However, in order to avoid the inclusion of carbon dioxide in the reaction system, it is preferable to carry out the reaction in a closed system. A simple method is to blow chlorine into a quaternary alkyl ammonium hydroxide solution prepared in a three-neck flask as shown in FIG. 1, which allows the reaction to proceed sufficiently and produces a quaternary alkyl ammonium hypochlorite solution with excellent storage stability. In addition, a reaction apparatus having a configuration shown in FIG. 2 may be used, as will be described in detail later.

In this embodiment, the amount of chlorine gas used (total amount of chlorine gas used) is not particularly limited, but is preferably 10 to 31,000 mL per 1 liter of quaternary alkyl ammonium hydroxide solution at 0 ° C. and 1 atm. By using chlorine gas in this range, a sudden pH change in the reaction system is suppressed, and it becomes easy to remove and reduce metal impurities by filtration. The amount of chlorine used can be more than 31,000 mL per 1 liter of quaternary alkyl ammonium hydroxide solution at 0 ° C. and 1 atm, but the pH of the quaternary alkyl ammonium hydroxide solution tends to decrease and fluctuate significantly, and unreacted chlorine gas tends to remain. On the other hand, if the amount is less than 10 mL, sufficient hypochlorite ions tend not to be generated. Therefore, considering industrial production, it is preferable that the amount of chlorine gas used is in the range of 10 to 31,000 mL per 1 liter of quaternary alkyl ammonium hydroxide solution at 0 ° C. and 1 atm. However, the amount of chlorine gas used can also be determined based on the pH of the resulting solution, i.e., the pH of the resulting quaternary alkyl ammonium hypochlorite solution.

In addition, it is preferable to supply chlorine gas into the reaction system at the following rate. The supply flow rate (rate) of chlorine gas is preferably 0.0034 Pa·m 3 /sec or more and 16.9 Pa·m 3 /sec or less ^per 1 liter of quaternary alkyl ammonium hydroxide solution, calculated at 0°C and 1 atm, in order not to cause ^a sudden drop in pH and to reduce chlorine gas not involved in the reaction. By satisfying this range, the reactivity becomes sufficient, and a quaternary alkyl ammonium hypochlorite solution can be produced without a sudden drop or change in pH. In order to further exert this effect, the supply amount of chlorine gas into the reaction system is more preferably 0.017 Pa·m ³ /sec or more and 5.1 Pa·m ³ /sec or less, and even more preferably 0.034 Pa·m ³ /sec or more and 1.7 Pa·m ³ /sec or less.

(Gas phase in reaction process)
The greatest feature of this embodiment is that the carbon dioxide concentration in the gas phase in the reaction step is 100 ppm by volume or less. In this embodiment, the gas phase refers to the portion occupied by the gas that comes into contact with the quaternary alkyl ammonium hydroxide solution in the reaction step, and for example, in the production method shown in Figure 1, it is the portion occupied by the gas in the three-neck flask 11 (the upper space).

In this embodiment, the upper limit of the carbon dioxide concentration in the gas phase is 100 ppm by volume. If the carbon dioxide concentration exceeds 100 ppm by volume, carbonate ions and bicarbonate ions are generated by the reactions of formulas (1) and (2) during the reaction step, and the pH of the quaternary alkyl ammonium hypochlorite solution decreases accordingly.

CO ₂ + OH ^- → HCO ₃ ^- ... (1)
HCO ₃ ⁻ + OH ⁻ → CO ₃ ²⁻ + H ₂ O … (2)

It is speculated that when the pH is lowered by the above chemical reaction, the hypochlorite ions decompose during storage of the resulting quaternary alkylammonium hypochlorite solution, resulting in a deterioration in storage stability.

In this embodiment, if the carbon dioxide concentration in the gas phase is 0.001 to 100 ppm by volume, preferably 0.01 to 80 ppm by volume, it becomes possible to adequately control the pH of the quaternary alkyl ammonium hypochlorite solution, and it is possible to produce a quaternary alkyl ammonium hypochlorite solution with excellent storage stability.

(pH of reaction process)
The pH range of the liquid phase in the reaction step of this embodiment is 10.5 or more. Although the upper limit is not particularly limited, if the pH during the reaction is excessively high, hypochlorite ions may be decomposed and the effective chlorine concentration may decrease if the solution is stored for a long period of time at the same pH after the reaction is completed. Therefore, the pH of the liquid phase in the reaction step is preferably less than 14, more preferably less than 13.9, and even more preferably 11 or more and less than 13.8. If the pH is within the above range, the decomposition of hypochlorite ions is suppressed during storage of the resulting quaternary alkyl ammonium hypochlorite solution, and the storage stability is improved. Even if the pH during the reaction is high, the storage stability is improved by controlling the pH during storage to a specific range as described below. On the other hand, if the pH of the reaction step is too low, the storage stability is reduced due to the chemical reaction shown in formula (3).

2HClO + ^ClO− + ^2OH− →
ClO ₃ ⁻ + 2Cl ⁻ + 2H ₂ O … (3)

(Reaction temperature in the reaction process)
The reaction temperature range of the quaternary alkylammonium hydroxide solution in the reaction step of this embodiment is preferably from −35° C. to 15° C., more preferably from −15° C. to 15° C., and even more preferably from 0° C. to 15° C. If the reaction temperature is within the above range, the quaternary alkylammonium hydroxide solution and chlorine react sufficiently, and the quaternary alkylammonium hypochlorite solution can be obtained with high production efficiency.

If the reaction temperature is below -35°C, the quaternary alkyl ammonium hydroxide solution will begin to solidify, and the reaction with chlorine will be insufficient. On the other hand, if the reaction temperature exceeds 15°C, the hypochlorite ions generated in the quaternary alkyl ammonium hydroxide solution will decompose due to heat. In particular, if the pH during the reaction is 13.8 or higher, the decomposition of hypochlorite ions will become more pronounced as the reaction temperature increases. The production efficiency of quaternary alkyl ammonium hypochlorite can be evaluated as the ratio of the number of moles of hypochlorite ions generated to the number of moles of chlorine molecules supplied as a raw material.

As described above, the manufacturing method of this embodiment makes it possible to produce a quaternary alkylammonium hypochlorite solution that has excellent storage stability and can adequately maintain its cleaning and removing power even 10 days after production.

As is clear from this, the quaternary alkyl ammonium hypochlorite solution obtained by the manufacturing method of this embodiment has excellent storage stability and can be suitably used in the manufacturing process of semiconductor devices.

<Second embodiment: Method for producing quaternary alkyl ammonium hypochlorite solution>
The second embodiment relates to a method for producing a quaternary alkyl ammonium hypochlorite solution, comprising a reaction step of contacting a quaternary alkyl ammonium hydroxide solution with chlorine gas in a reaction vessel;
The surface of the reaction vessel that comes into contact with the quaternary alkyl ammonium hydroxide solution is made of an organic polymer material.

(Quaternary alkyl ammonium hydroxide solution and chlorine gas)
The quaternary alkyl ammonium hydroxide solution and chlorine gas may be the same as those described in the first embodiment.

(Reaction conditions: Organic polymer material used on the inner surface of the reaction vessel)
In this embodiment, the quaternary alkyl ammonium hydroxide solution is contacted with the chlorine gas in a reaction vessel to produce a quaternary alkyl ammonium hypochlorite solution. At this time, a predetermined amount of the quaternary alkyl ammonium hydroxide solution is first introduced into the reaction vessel, and then chlorine gas is introduced so as to contact the quaternary alkyl ammonium hydroxide solution.

In this embodiment, the surface in the reaction vessel that comes into contact with the quaternary alkyl ammonium hydroxide solution (hereinafter, sometimes simply referred to as the "inner surface of the reaction vessel") is formed from an organic polymer material. According to the inventors' studies, when a general-purpose borosilicate glass (hereinafter, glass) reaction vessel is used as the reaction vessel, the quaternary alkyl ammonium hydroxide solution used as the raw material dissolves metal components contained in the glass, such as sodium, potassium, and aluminum. This is thought to be due to the alkaline nature of the quaternary alkyl ammonium hydroxide solution used as the raw material. Therefore, by forming the inner surface of the reaction vessel from an organic polymer material, it is possible to reduce the inclusion of impurities containing the above metals (metal impurities).

In this embodiment, when an organic solvent is used as the solvent, it is preferable that the reaction apparatus has an explosion-proof structure. Therefore, in order to simplify the apparatus configuration, it is preferable that the quaternary alkyl ammonium hydroxide solution uses water as the solvent.

In this embodiment, the organic polymer material used may be vinyl chloride resin (soft and hard vinyl chloride resin), nylon resin, silicone resin, polyolefin resin (polyethylene, polypropylene), fluorine resin, etc. Among them, fluorine resin is recommended in consideration of ease of molding, solvent resistance, and low elution of impurities.

The fluororesin is not particularly limited as long as it is a resin (polymer) containing fluorine atoms, and known fluororesins can be used. Examples include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, chlorotrifluoroethylene-ethylene copolymer, and cyclized polymer of perfluoro(butenyl vinyl ether). Among these, it is preferable to use tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, taking into consideration the availability of the reaction vessel itself, productivity, and the like.

In this embodiment, methods for forming the inner surface of the reaction vessel from an organic polymer material include a method for forming the entire reaction vessel from an organic polymer material, and a method for covering only the inner surface of a glass or stainless steel reaction vessel with an organic polymer material.

In addition, the organic polymer material can be washed before use to prevent metal components from eluting from the material. Specifically, it is preferable to thoroughly wash the material with an acid such as high-purity nitric acid or hydrochloric acid (for example, by immersing the material in a solution with an acid concentration of 1 mol/L for 12 hours), and then further wash the material with ultrapure water or the like. In order to perform a stable reaction, it is preferable to wash the inner surface of the reaction vessel formed from the organic polymer material by the above-mentioned method before reacting the quaternary alkyl ammonium hydroxide solution with chlorine gas.

In this embodiment, as long as the surface in the reaction vessel that comes into contact with the quaternary alkylammonium hydroxide solution is made of an organic polymer material, the other parts may be made of glass, stainless steel, or passivated stainless steel. However, since the effect is small, it is preferable to form the stirring rod and the like from the same organic polymer material, although this is not essential.

In this embodiment, the quaternary alkyl ammonium hydroxide solution may be brought into contact with chlorine gas in a reaction vessel, but it is preferable to introduce chlorine gas into the quaternary alkyl ammonium hydroxide solution while stirring. The reaction temperature range is not particularly limited, but is preferably the same as in the first embodiment.

In addition, when carbon dioxide is present in the reaction system, the pH of the resulting quaternary alkyl ammonium hypochlorite solution tends to decrease. Therefore, in consideration of stable production, it is preferable to prevent carbon dioxide from being contained in the reaction system, as in the first embodiment. Specifically, it is preferable to use a quaternary alkyl ammonium hydroxide solution or chlorine gas with a reduced amount of carbon dioxide. It is also preferable to carry out the reaction in the presence of an inert gas with a reduced amount of carbon dioxide (for example, in the presence of nitrogen gas). By carrying out the reaction under such conditions, the decrease in pH of the resulting quaternary alkyl ammonium hypochlorite solution can be suppressed, thereby improving storage stability.

(Reaction Apparatus)
Next, an example of a reaction apparatus that can be suitably used in this embodiment will be described. A schematic diagram of the reaction apparatus 31 is shown in FIG.

In the reaction device 31, the surface (inner surface of the reaction container) 34 of the reaction container 32 that comes into contact with the quaternary alkyl ammonium hydroxide solution 33 is formed from the organic polymer material. The reaction device 31 can also be provided with a thermometer (thermocouple) 35 that can check the temperature. It is preferable to provide a stirring motor 36, stirring rod 37, and stirring blade 38 so that the reaction system can be mixed. The thermometer 35, stirring rod 37, and stirring blade 38 are also preferably formed from an organic polymer material in the parts that come into contact with the quaternary alkyl ammonium hydroxide solution 33.

The reaction device 31 may be provided with a chlorine gas supply pipe 39 for supplying chlorine gas, and the chlorine gas may be brought into contact with the quaternary alkyl ammonium hydroxide solution 33 via a gas introduction pipe 40 for introducing chlorine gas into the reaction system through the supply pipe 39. As described above, it is preferable that the reaction system does not contain carbon dioxide, so a nitrogen gas supply pipe 41 may also be provided. In FIG. 2, the nitrogen gas supply pipe 41 merges with the chlorine gas supply pipe 39 midway, and nitrogen gas is introduced from the gas introduction pipe 40, but the gas introduction pipe 40 may be separated into a chlorine gas introduction pipe/nitrogen gas introduction pipe. Since the gas introduction pipe 40 comes into contact with the quaternary alkyl ammonium hydroxide solution 33, it is preferable that the gas introduction pipe 40 is formed from the organic polymer material.

As described in detail below, in this embodiment, when chlorine gas is brought into contact with a quaternary alkyl ammonium hydroxide solution to produce a quaternary alkyl ammonium hypochlorite solution, the pH in the reaction system may decrease, and solid matter containing metal components may precipitate. In this embodiment, a filtration device may be provided to remove and reduce the solid matter by filtration. This filtration device includes a reaction liquid transfer pipe 42, a pump 43, a filtration filter 44, and a reaction liquid return pipe 45. Each of these components in the filtration device is preferably formed of the organic polymer material, since it comes into contact with the reaction solution containing the quaternary alkyl ammonium hypochlorite.

The pump 43 can be a chemical diaphragm pump, a tube pump, a magnetic pump, or the like. Among them, it is preferable to use a pump whose liquid-contacting parts are made of the above-mentioned fluororesin to prevent contamination by metal components, and among them, it is preferable to use a magnetic pump considering ease of availability.

The filter 44 is preferably made of the material and has the shape described in detail below. In FIG. 2, an example in which one filter 44 is provided is shown, but multiple filters 44 can also be arranged in series and/or parallel depending on the intended use (impurities to be removed).

By providing a filtration device as described above, it is also possible to perform a filtration operation during the reaction. In addition, the supply of chlorine gas can be stopped, and after the reaction, a solution containing quaternary alkyl ammonium hypochlorite can be circulated using pump 43, and solid matter containing metal components can be removed or reduced using filter 44. Note that while Figure 2 shows a configuration in which the reaction device and filtration device are integrated, the reaction device and filtration device may be installed separately if filtration is performed after the reaction.

It is also possible to provide a chlorine gas exhaust pipe 46 and a chlorine gas trap 47 for releasing the unreacted chlorine gas that has been supplied. The chlorine gas trap 47 may contain, for example, a 5% by mass aqueous solution of sodium hydroxide.

In addition, a reaction bath 48 can be provided around the reaction vessel 32 to control the reaction temperature.

The thermometer 35, stirring rod 37, gas inlet pipe 40, reaction liquid transfer pipe 42, reaction liquid return pipe 45 and chlorine gas exhaust pipe 46 can be connected to the reaction vessel 32 by a half joint 49 or the like.

By using such a reaction apparatus 31, the method of this embodiment can be easily carried out, and a highly pure quaternary alkyl ammonium hypochlorite solution can be produced.

<Filtration process>
When the quaternary alkyl ammonium hydroxide solution and chlorine gas come into contact with each other to produce a quaternary alkyl ammonium hypochlorite solution, the pH of the solution in the reaction system drops. At that time, solid matter containing metal impurities may precipitate, and in order to remove or reduce it, in a preferred embodiment, it is preferable to include a filtering step. That is, it is preferable to filter the quaternary alkyl ammonium hypochlorite solution obtained by supplying chlorine gas to a predetermined concentration during the reaction of the first and second embodiments. The filtering step may be performed after the storage step or dilution step described below.

In the filtration step, the metal components filtered out may vary depending on the pH of the quaternary alkylammonium hypochlorite solution.
Specifically, when the pH of the quaternary alkylammonium hypochlorite solution is 13.5 or less, preferably when the pH of the solution is greater than 12.5 and less than 13.5, hydroxides of magnesium, iron, cadmium, etc., and oxides of nickel and silver are solidified, and these impurities can also be removed or reduced by performing a filtration operation.

In addition, when the pH of the quaternary alkylammonium hypochlorite solution is 12.5 or less, preferably when the pH of the solution is 9.0 or more and 12.5 or less, in addition to the above impurities, copper and lead oxides are solidified, and these impurities can also be removed or reduced by performing a filtration operation. Note that the pH of the solution may vary depending on the temperature. The above pH is based on the value at 25°C. The liquid temperature when actually carrying out the filtration process is not limited to 25°C, but is preferably 20 to 28°C, and more preferably 23 to 25°C.

Such solid metal impurities are produced even when the purity of the raw material quaternary alkyl ammonium hydroxide solution and chlorine gas is increased. In particular, such solids may be produced when the inner surface of the reaction vessel is made of an organic polymer material. The reason for this is unclear, but it is presumed that metal impurities are contained in the reaction system from somewhere inside the reaction apparatus due to the use of highly corrosive gas, chlorine gas.

The filtration operation may be performed at a pH at which the metals to be removed or reduced are solidified. Therefore, it may be performed only once, or multiple times at each pH. In this case, multiple filtration filters with different pore sizes are prepared for each pH, and filtration is performed in order from the filter with the largest pore size, thereby improving the filtration efficiency. Specifically, it is possible to remove coarse particles in the first stage and fine particles in the second stage. Note that, among solid substances containing metal components, such as simple metal impurities, metal oxides, metal hydroxides, and/or colloidal substances, particles of 1 μm to 100 μm may be referred to simply as "coarse particles" below. On the other hand, particles of 0.01 μm to less than 1 μm may be referred to simply as "fine particles" below. Note that the particle size of a solid substance refers to the circle equivalent diameter by laser diffraction.

The filtering operation is not particularly limited, and can be carried out using a known filtering device and filter. However, in order to avoid increasing unnecessary metal components, it is preferable that the surfaces of the filtering device that may come into contact with the quaternary alkylammonium hypochlorite solution are made of an organic polymer material. The organic polymers that can be used are the same as those exemplified above.

As a specific filtration filter, it is preferable to use a filtration filter made of an organic polymer material or an inorganic material. For example, filtration filters made of polyolefin (polypropylene, polyethylene, ultra-high molecular weight polyethylene), polysulfone, cellulose acetate, polyimide, polystyrene, the above-mentioned fluorine-based resin, and/or quartz fiber can be mentioned. In addition, it is preferable to use a filtration filter in combination with a positively charged membrane and a negatively charged membrane. The reason for this is that many metal oxides and metal hydroxides are negatively charged in an alkaline atmosphere, and a positively charged filtration filter by electrostatic adsorption can effectively remove metal components. In addition, some metal components exist in a cationic state and are positively charged. For this reason, a negatively charged filtration filter can effectively remove ionized metal components by electrostatic adsorption.

The pore size of the filter is not particularly limited, but a filter with a pore size of 1 μm or more, or a precision filter, can be used to remove coarse particles. On the other hand, a precision filter with a pore size of 0.01 μm or more and less than 1 μm, an ultrafilter, or a nanofiltration membrane can be used to remove fine particles.

The above-mentioned filters can be commercially available. Specifically, the polytetrafluoroethylene "Fluoroguard ATX filter (pore size 0.05 μm)," "Quick Change ATE filter (pore size 0.03 μm)," "Torrent ATE filter (pore size 0.02 μm)," and "Fluoroline P-1500 (pore sizes 0.05 μm, 0.1 μm)" manufactured by Nippon Entegris Co., Ltd. can be used.

The above filtration operation can be performed before adjusting the pH of the quaternary alkyl ammonium hypochlorite solution to a range suitable for its application. In this case, after performing the filtration operation once, it can be mixed with chlorine gas again to obtain a quaternary alkyl ammonium hypochlorite solution of the desired pH. It is also possible to obtain a quaternary alkyl ammonium hypochlorite solution of the desired pH by mixing with water, an acid such as hydrogen chloride, and/or an alkali such as an aqueous solution of quaternary tetramethylammonium hydroxide. On the other hand, if the pH of the produced quaternary alkyl ammonium hypochlorite solution is suitable for use as a cleaning solution, the solution can be filtered and used as it is as a cleaning solution for manufacturing semiconductor devices.

By performing such a filtration operation, it is possible to reduce metal components, particularly magnesium, iron, nickel, copper, silver, cadmium, and lead.

<Preservation process>
The quaternary alkyl ammonium hypochlorite solution after the reaction step in the first and second embodiments or after the filtration step can be used as is for a specific purpose such as a cleaning solution, but is generally used after a preservation step (including storage and transportation). The quaternary alkyl ammonium hypochlorite solution alone has poor storage stability, and the addition of a stabilizer has been required. However, the stabilizer can cause organic residues, and improvements have been required, but by going through the preservation step described below, it is possible to supply a quaternary alkyl ammonium hypochlorite solution with improved storage stability.

The method for producing a quaternary alkyl ammonium hypochlorite solution according to a preferred embodiment of the present invention includes a storage step of storing the reaction solution after the reaction step, and in the storage step, the pH of the quaternary alkyl ammonium hypochlorite solution at 25°C is adjusted to 12.0 or more and less than 14.0. Note that a filtration step may be performed after the reaction step, and then the storage step may be performed.

The concentration of the quaternary alkylammonium hypochlorite solution to be preserved is not particularly limited, but considering industrial production, it is preferable for the quaternary alkylammonium hypochlorite solution to contain 0.001 to 20% by mass of hypochlorite ions and 0.001 to 50% by mass of quaternary alkylammonium ions at a specified pH. Note that the "specified pH" refers to any pH between 12.0 and less than 14.0 selected as the pH in the preservation process.

In addition, various additives may be added to the quaternary alkylammonium hypochlorite solution as desired depending on the application. For example, additives such as metal chelating agents, complexing agents, metal dissolution promoters, metal corrosion inhibitors, surfactants, acids, and alkalis can be added. The addition of these additives is expected to promote or inhibit metal dissolution during semiconductor wafer processing, improve surface roughness, increase processing speed, and reduce particle adhesion, so cleaning solutions containing these additives can be suitably used for semiconductor wafer processing.

In a preferred embodiment, the method for storing a quaternary alkyl ammonium hypochlorite solution stores the quaternary alkyl ammonium hypochlorite solution in a limited pH range. The storage method is described in detail below.

Here, "storage" refers to the period from when storage of the quaternary alkyl ammonium hypochlorite solution begins when the pH at 25°C is between 12 and 14, until the concentration and/or pH of the quaternary alkyl ammonium hypochlorite solution is adjusted. If the pH of the solution after the pH adjustment is between 12 and 14, further storage of the solution also falls under the storage of the present invention. If the pH of the quaternary alkyl ammonium hypochlorite solution is between 12 and 14 from the beginning, it may be stored as is, and if the pH is less than 12 or 14 or greater, it may be stored after adjusting the pH to a range between 12 and 14.

The pH of the solution may vary depending on the temperature. The above pH is based on the value at 25°C. The temperature at which the solution is actually stored is not limited to 25°C. Therefore, the storage conditions are not particularly limited, but it is preferable to store the solution under general storage conditions, i.e., at -25 to 50°C in a known container, a canister can, or a plastic storage container, and it is even more preferable to store the solution in a dark place at -20 to 40°C in a light-shielding storage container, a transport container such as a canister can, or a plastic storage container filled with inert gas. If the storage temperature exceeds the above range, hypochlorite ions may thermally decompose to form oxygen molecules during long-term storage, causing the container to expand and even break.

In a preferred embodiment, the solution is stored as a quaternary alkyl ammonium hypochlorite solution having a pH of 12 or more and less than 14 at 25°C. If the pH is within this range, the hypochlorite ion concentration does not decrease and long-term storage is possible. If the pH is less than 12, the disproportionation reaction of hypochlorite ions proceeds, the hypochlorite ions are decomposed, and the oxidizing power of the quaternary alkyl ammonium hypochlorite solution decreases. On the other hand, if the pH is 14 or more, it is estimated that the organic ions, which are cations, decompose. As a result, it is estimated that the disproportionation reaction of hypochlorite ions inhibited by the bulkiness of the organic ions proceeds again, and the hypochlorite ions decompose. It is preferable to store the solution as a quaternary alkyl ammonium hypochlorite solution having a pH of 12 or more and less than 13.9 at 25°C, and more preferably to store the solution at a pH of 12 or more and less than 13.8 at 25°C.

The reason why the storage stability is improved by the above-mentioned storage method is unclear, but the inventors speculate as follows. In the quaternary alkyl ammonium hypochlorite solution, some of the quaternary alkyl ammonium hypochlorite is dissociated into hypochlorite ions and organic ions, but most of the hypochlorite ions are ionic bonds with the organic ions, and it is speculated that the three-dimensional bulkiness of the organic ions suppresses the disproportionation reaction of the hypochlorite ions. For this reason, it is believed that the greater the three-dimensional bulkiness of the organic ions, the more the disproportionation reaction is suppressed and the better the storage stability. If the organic ion is a bulky quaternary alkyl ammonium ion, such as a tetramethylammonium ion, the disproportionation reaction can be sufficiently suppressed.

According to the storage method of the present invention, the oxidizing power of the quaternary alkyl ammonium hypochlorite solution during storage hardly changes, even if the storage period is 30 days, preferably 60 days, or even more preferably 90 days. Therefore, after storage, the quaternary alkyl ammonium hypochlorite solution can be used for various purposes simply by diluting it depending on the conditions of use. The longer the storage period, the greater the effect of improving productivity can be expected.

(Dilution process)
The quaternary alkyl ammonium hypochlorite solution may be appropriately diluted according to its application. In the dilution step, the quaternary alkyl ammonium hypochlorite solution is stored at pH 12 or more through the above-mentioned storage step, and then the quaternary alkyl ammonium hypochlorite solution is diluted with a solution having a pH of less than 12, and the pH is adjusted to 8.0 or more and less than 12.0.

The method for diluting the quaternary alkyl ammonium hypochlorite solution may be any method capable of relatively increasing the hydrogen ion concentration contained in the quaternary alkyl ammonium hypochlorite solution, and the quaternary alkyl ammonium hypochlorite solution may be diluted with water, with a solution containing an acid, or with a solution having a lower pH than the pH of the quaternary alkyl ammonium hypochlorite solution during storage. For example, an example of a solution having a lower pH than the quaternary alkyl ammonium hypochlorite solution stored by the storage method of the present invention is an alkaline solution, for example, a quaternary alkyl ammonium hydroxide solution having a pH of less than 12.

The solution added to dilute the quaternary alkyl ammonium hypochlorite solution may or may not contain quaternary alkyl ammonium hypochlorite. For example, when diluting with a solution containing quaternary alkyl ammonium hypochlorite, not only can the pH be adjusted but also the concentration of the quaternary alkyl ammonium hypochlorite solution can be adjusted as desired.

In the present invention, the solution added to dilute the quaternary alkyl ammonium hypochlorite solution is preferably a solution having a pH greater than 0 and equal to or less than 7. By using an acidic solution, the decrease in concentration of quaternary alkyl ammonium hypochlorite due to pH adjustment can be reduced. Specific examples of solutions having a pH greater than 0 and equal to or less than 7 include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, hydrofluoric acid, bromic acid, chloric acid, perchloric acid, iodic acid, periodic acid, and carbonic acid, and organic acids such as formic acid, acetic acid, glacial acetic acid, propionic acid, citric acid, oxalic acid, malic acid, lactic acid, and benzoic acid.

In addition, if the solution used for dilution has a high impurity concentration, the applications of the resulting diluted solution are limited, so it is preferable for the solution used for dilution to have a low impurity content. For example, when using a quaternary alkyl ammonium hypochlorite solution as a processing solution for semiconductor wafers, high purity is required, so it is preferable to dilute the high-purity quaternary alkyl ammonium hypochlorite solution with hydrochloric acid, sulfuric acid, or the like, which can be easily purified industrially.

The method for diluting the quaternary alkyl ammonium hypochlorite solution is not particularly limited, and dilution may be performed by a known method. For example, a method may be used in which the quaternary alkyl ammonium hypochlorite solution and the solution used for dilution are supplied from two supply ports of the container, respectively, and mixed by stirring using a propeller or rotor, or a method may be adopted in which the liquid is circulated using a pump to mix. In addition, the solution used for dilution may be supplied to a container in which the quaternary alkyl ammonium hypochlorite solution is stored, to dilute the solution.

As another dilution method, the quaternary alkyl ammonium hypochlorite solution can be diluted by mixing the quaternary alkyl ammonium hypochlorite solution with a solution used for dilution at the location where the quaternary alkyl ammonium hypochlorite solution-containing composition is used. For example, dilution can be performed at the point of use by supplying the quaternary alkyl ammonium hypochlorite solution and the solution used for dilution from two nozzles, respectively. This method is particularly effective when processing semiconductor wafers.

In addition, when the diluted solution is used for semiconductor cleaning, a method of diluting the quaternary alkyl ammonium hypochlorite solution by adding an inorganic acid or an organic acid can be adopted. The dilution is performed by merging the pipe supplying the quaternary alkyl ammonium hypochlorite solution with the pipe supplying the inorganic acid or the organic acid midway and mixing them, and the resulting diluted solution is supplied to the semiconductor wafer, which is the surface to be cleaned. This mixing can be performed by a method in which the liquids are mixed by collision through a narrow passage under pressure; a method in which the pipe is filled with a filler such as a glass tube and the flow of the liquid is repeatedly divided, separated, and merged; or a method in which a blade that rotates by power is provided in the pipe.

As described above, by adopting the dilution process, it is possible to use a diluted solution that stably maintains its oxidizing power compared to when the quaternary alkyl ammonium hypochlorite solution is stored at the pH at which it will be used. Generally, when using a quaternary alkyl ammonium hypochlorite solution as a cleaning solution, the pH is diluted to about 8 to 12. However, if the quaternary alkyl ammonium hypochlorite solution is stored at this pH, the hypochlorite ion concentration decreases and the cleaning properties decrease. However, by storing the solution through the above storage process and then through the above dilution process, a diluted solution (cleaning solution) with a high hypochlorite ion concentration can be obtained.

(Method of Processing Semiconductor Wafer)
The processing method of the present invention is a processing method capable of etching, cleaning, and removing various metals and their compounds present on a semiconductor wafer without damaging the semiconductor wafer. However, the subject of the processing is not limited to this, and the processing method can be used to clean semiconductor wafers that do not have metals on their surfaces, and can also be used for wet etching of metals.

The subject of the treatment method of the present invention is preferably a semiconductor wafer having at least one compound selected from the group consisting of copper, tungsten, tantalum, titanium, cobalt, ruthenium, manganese, aluminum, silicon, silicon oxide, and compounds thereof. Since the present invention can effectively exert the strong oxidizing action of hypochlorite ions, it can be suitably used for treating precious metals that are not easily oxidized among the above metals. Therefore, the treatment method of the present invention can be suitably used when cleaning and removing precious metals, particularly ruthenium. For example, when cleaning and removing ruthenium, a known cleaning method can be adopted.

As described above, the storage method of the present invention can provide a quaternary alkyl ammonium hypochlorite solution that can adequately maintain its cleaning and removing power even 30 days after production. In this way, by providing a quaternary alkyl ammonium hypochlorite solution with excellent storage stability, the costs associated with transporting and storing the quaternary alkyl ammonium hypochlorite solution can be reduced, which is of great industrial importance.

<Quaternary alkyl ammonium hypochlorite solution>
By going through the manufacturing method of the second embodiment and the filtration process, a quaternary alkyl ammonium hypochlorite solution with reduced metal component content can be manufactured. Of course, the solvent of the quaternary alkyl ammonium hypochlorite solution is the same as the solvent of the quaternary alkyl ammonium hydroxide solution, which is the raw material, but other solvents can also be added within a range that does not impair the effects of the present invention. However, considering operability, ease of handling, versatility, etc., the solvent of the quaternary alkyl ammonium hypochlorite solution is preferably water.

By using the manufacturing method of the second embodiment and the filtration process, the resulting quaternary alkylammonium hypochlorite solution can have metal components, specifically, sodium, potassium, and aluminum, each of which is less than 1 ppb (by mass). The contents of these metal components are values measured by inductively coupled plasma mass spectrometry as shown in the examples.

Furthermore, by carrying out the filtration operation described above, the resulting quaternary alkylammonium hypochlorite solution can have magnesium, iron, nickel, copper, silver, cadmium, and lead contents of less than 1 ppb (by mass). The contents of these metal components are also values measured by inductively coupled plasma mass spectrometry as shown in the examples.

Therefore, most preferably, the quaternary alkyl ammonium hypochlorite solution contains less than 1 ppb of each of sodium, potassium, aluminum, magnesium, iron, nickel, copper, silver, cadmium, and lead. The form of the metal components in the quaternary alkyl ammonium hypochlorite solution is not particularly limited, and they may be contained as metal atoms or ions, or may be in the form of fine particles such as oxides or hydroxides, complexes, etc.

The pH of the resulting quaternary alkyl ammonium hypochlorite solution is not particularly limited and may be appropriately determined depending on the intended use. For example, if the pH is greater than 12.5, it can be used as a photoresist remover (developer) or for planarizing precious metal layers when forming semiconductor elements.

In particular, by adjusting the pH to 9.0 or more and 12.5 or less, the resulting quaternary alkyl ammonium hypochlorite solution can also be used for etching precious metals. In this case, the pH can be adjusted to 9.0 or more and 12.5 or less while supplying chlorine gas to the quaternary alkyl ammonium hydroxide solution with a high pH, making it easy to manufacture. In addition, by performing a filtration operation during or after manufacture, it is possible to further reduce the content of metal components.

The quaternary alkyl ammonium hypochlorite solution obtained by the present invention can also be blended with known additives such as common stabilizers such as benzotriazoles, benzophenones, oxanilides, and salicylates. The addition of such stabilizers improves storage stability.

Next, the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to the examples. First, the measuring device used and the manufacturing method of each component will be described.

<pH measurement method>
The pH of each of the quaternary alkyl ammonium hydroxide solution and the quaternary alkyl ammonium hypochlorite solution (30 mL) was measured using a tabletop pH meter (LAQUA F-73, manufactured by Horiba, Ltd.) The pH measurement was performed after the solution was stabilized at 23°C.

<How to calculate available chlorine concentration and hypochlorite ion concentration>
To prepare the quaternary alkylammonium hypochlorite solution, 0.5 mL of the treatment solution, 2 g of potassium iodide (Fujifilm Wako Pure Chemical Industries, special grade reagent), 8 mL of 10% by mass acetic acid, and 10 mL of ultrapure water were added to a 100 mL Erlenmeyer flask and stirred until the solids were dissolved to obtain a brown solution.

The brown solution thus prepared is subjected to redox titration using 0.02 M sodium thiosulfate solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric analysis) until the color of the solution changes from brown to very pale yellow, and then starch solution is added to obtain a pale purple solution.

0.02 M sodium thiosulfate solution was then added to this solution, and the effective chlorine concentration was calculated using the point at which the solution became colorless and transparent as the end point. The hypochlorite ion concentration was also calculated from the effective chlorine concentration obtained. For example, if the effective chlorine concentration is 1% by mass, the hypochlorite ion concentration is 0.73% by mass.

<Calculation method for carbon dioxide concentration in the gas phase>
The carbon dioxide concentration in the gas phase of the reaction solution was measured using a CO ₂ monitor (CO ₂ -M1, manufactured by CUSTOM).

<Reaction efficiency>
The reaction efficiency was calculated from the ratio (%) of the number of moles of hypochlorite ions generated to the number of moles of chlorine molecules supplied. If the entire amount of chlorine added reacts (no decomposition occurs), the reaction efficiency is 100%. If hypochlorite ions decompose during the reaction, the reaction efficiency decreases.

<Evaluation method 1 for storage stability>
The quaternary alkyl ammonium hypochlorite solution is transferred into a glove bag, and after the carbon dioxide concentration in the glove bag becomes 1 ppm or less, it is transferred into a PFA container and sealed.Then, after storing in a light-shielded environment at 23°C for 10 days, the hypochlorite ion concentration of the quaternary alkyl ammonium hypochlorite solution in the PFA container is measured.The hypochlorite ion concentration ratio (concentration after 10 days/initial concentration) is rated as good if it is 60% or more and 100% or less, and as bad if it is less than 60%.

<Evaluation method 2 for storage stability>
The tetramethylammonium hypochlorite solution is transferred into a glove bag, and after the carbon dioxide concentration in the glove bag becomes 1 ppm or less, it is transferred into a PFA container. Next, the carbon dioxide concentration is 1 ppm or less, and after storing in a light-shielded environment at 23°C for 30 days, the hypochlorite ion concentration in the tetramethylammonium hypochlorite solution in the PFA container is measured. A hypochlorite residual rate (hypochlorite ion concentration after 30 days/initial hypochlorite ion concentration) of 50% or more is considered good, and a hypochlorite residual rate of less than 50% is considered bad because it may cause problems that make it difficult to use in practical use.

<Calculation method for ruthenium etching rate>
An oxide film was formed on a silicon wafer using a batch-type thermal oxidation furnace, and a ruthenium film of 200 Å (±10%) was formed thereon using a sputtering method. The sheet resistance was measured using a four-point probe resistance meter (Loresta-GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and converted into a film thickness. Specifically, 30 ml of the obtained tetramethylammonium hypochlorite solution was prepared in a beaker, and then the tetramethylammonium hypochlorite solution with a pH of more than 12 was diluted with an inorganic acid or an organic acid to a desired pH to obtain a measurement solution. Each sample piece of a ruthenium-attached wafer cut to 10×20 mm was immersed in this measurement solution for 1 minute, and the change in film thickness before and after the treatment was divided by the immersion time to calculate the etching rate, which was evaluated as the ruthenium etching rate. It is known that the etching rate becomes slower as the pH increases. Therefore, the range that can be practically used at each pH was determined as follows. At pH 9.1, a ruthenium etching rate of 300 Å/min or more was evaluated as good, and less than 300 Å/min was evaluated as bad. At pH 9.5, a rate of 100 Å/min or more was rated as good, and a rate of less than 100 Å/min was rated as bad.At pH 10.5, a rate of 20 Å/min or more was rated as good, and a rate of less than 20 Å/min was rated as bad.At pH 11.0, a rate of 5 Å/min or more was rated as good, and a rate of less than 5 Å/min was rated as bad.

<Method for measuring metal concentration in quaternary alkyl ammonium hypochlorite solution>
High-resolution inductively coupled plasma mass spectrometry was used to measure the metal concentrations in the quaternary alkylammonium hypochlorite solutions.

Ultrapure water and 1.25 mL of high-purity nitric acid (Ultrapure-100 nitric acid, manufactured by Kanto Chemical Co., Ltd.) were added to a 25 mL polyfluoroalkyl ether (PFA) measuring flask (AsOne, PFA measuring flask). Next, 0.25 mL of quaternary alkyl ammonium hypochlorite solution was collected using a pipette (AsOne, Pipetman P1000) and a fluororesin pipette tip (AsOne, fluororesin pipette tip), added to the PFA measuring flask and stirred. Next, the measurement sample was prepared by diluting the solution 100 times with ultrapure water. Furthermore, the amount of metal was quantified by the calibration curve method using a high-resolution inductively coupled plasma mass spectrometer (ThermoFisher Scientific, Element2). In order to confirm the increase or decrease in sensitivity due to the matrix, a measurement solution to which impurities were added to make 2 ppb was also measured. The measurement conditions were RF output of 1500 W, argon gas flow rate of plasma gas of 15 L/min, auxiliary gas of 1.0 L/min, and nebulizer gas of 0.7 L/min.

Example 1
<Preparation of tetramethylammonium hypochlorite solution>
253 g of 25 mass% tetramethylammonium hydroxide (TMAH) aqueous solution with a _CO2 content of 2 ppm and 747 g of ion-exchanged water were mixed in a 2 L glass three-neck flask (manufactured by Cosmos Bead Co., Ltd.) to obtain a TMAH aqueous solution with a _CO2 content of 0.5 ppm and a CO2 content of 6.3 mass%. The pH at this time was 13.8. The _CO2 concentration in the laboratory was 350 ppm.

Next, as shown in Fig. 1, a rotor 14 (AsOne, total length 30 mm x diameter 8 mm) was placed in a three-neck flask 11, a thermometer protection tube 12 (Cosmos Bead, bottom-sealed type) and a thermocouple 13 were placed in one opening, a chlorine gas cylinder and a nitrogen gas cylinder were connected to the other opening, and the tip of a PFA tube 15 (Flon Industries, F-8011-02) that was connected to a state in which chlorine gas/nitrogen gas could be switched at will was immersed in the bottom of the solution, and the remaining opening was connected to a gas washing bottle 16 (AsOne, gas washing bottle, model number 2450/500) filled with a 5% by mass aqueous sodium hydroxide solution 17. Next, nitrogen gas with a carbon dioxide concentration of less than 1 ppm was flowed from the PFA tube at 0.289 Pa·m ³ /sec (at 0°C) for 20 minutes to expel carbon dioxide from the gas phase. At this time, the carbon dioxide concentration in the gas phase in the flask was 1 ppm or less.

Thereafter, a magnetic stirrer (AsOne Corp., C-MAG HS10) was placed at the bottom of the three-neck flask and rotated and stirred at 300 rpm, and while the outer periphery of the three-neck flask was cooled with ice water 10, chlorine gas (Fujiox Corp., specified purity 99.4%) was supplied at 0.064 Pa·m ³ /sec (at 0°C) for 180 minutes to obtain a tetramethylammonium hypochlorite solution. At this time, the liquid temperature during the reaction was 11°C.

The resulting solution was placed in a three-necked glass flask and transferred into a glove bag to avoid contact with the air. After the carbon dioxide concentration in the glove bag reached 1 ppm or less, the solution was transferred into a 1 L PFA container.

<Evaluation>
In a glove bag where the carbon dioxide concentration was 1 ppm or less, 30 mL of the obtained tetramethylammonium hypochlorite aqueous solution was poured into a fluororesin container, and the pH and available chlorine concentration were evaluated, and it was confirmed that the pH was 13.0 and the hypochlorite ion concentration was 1.59 mass%.

Next, 30 mL of the aqueous solution of tetramethylammonium hypochlorite that had been stored for 10 days in an environment with a carbon dioxide concentration of 1 ppm or less and a storage temperature of 23°C was poured into a fluororesin container, and the pH and available chlorine concentration were evaluated. At this time, the pH was 13.0 and the hypochlorite ion concentration was 1.59 mass%, confirming that the pH and available chlorine concentration had not changed significantly.

<Examples 2 to 7>
In Examples 2 to 7, tetramethylammonium hypochlorite solutions were prepared and evaluated in the same manner as in Example 1, except that (A) the mass concentration of the TMAH solution, (B) the pH of the TMAH solution, (C) the amount of chlorine supplied, (D) the supply rate, (E) the reaction temperature, and (F) the carbon dioxide concentration in the gas phase were adjusted to satisfy the conditions shown in Table 1. In Example 7, cooling was not performed during the reaction, and the reaction temperature was increased from 25° C. to 35° C.

<Comparative Example 1>
233 g of a 25% by mass TMAH aqueous solution with a _CO2 content of 2 ppm and 767 g of ion-exchanged water were mixed in a 2 L glass beaker (manufactured by AsOne) to obtain a 5.8% by mass TMAH aqueous solution. The pH at this time was 13.8. Next, as shown in FIG. 3, a rotor 24 (manufactured by AsOne, total length 30 mm x diameter 8 mm) was placed in a glass beaker 21, followed by a thermometer protection tube 22 (manufactured by Cosmos Bead, bottom-sealed type) and a thermocouple 23, and the tip of a PFA tube 25 (manufactured by Flon Industries, F-8011-02) connected to a chlorine gas cylinder was immersed in the bottom of the solution. At this time, the carbon dioxide concentration in the gas phase was 350 ppm.

Thereafter, a magnetic stirrer (AsOne Corp., C-MAG HS10) was placed under the glass beaker and rotated at 300 rpm, while the outer periphery of the glass beaker was cooled with ice water 28 and chlorine gas (Fujiox Corp., specified purity 99.4%) was supplied at 0.064 Pa·m ³ /sec (at 0° C.) for 180 minutes to obtain a tetramethylammonium hypochlorite solution. At this time, the liquid temperature during the reaction was 11° C.

The resulting solution was transferred into a glove bag to avoid contact with the air, and after the carbon dioxide concentration in the glove bag reached 1 ppm or less, it was transferred into a 1 L PFA container.

<Comparative Examples 2 to 3>
In Comparative Examples 2 and 3, a tetramethylammonium hypochlorite solution was prepared and evaluated in the same manner as in Comparative Example 1, except that (A) the mass concentration of the tetramethylammonium hydroxide solution, (B) the pH of the tetramethylammonium hydroxide solution, (C) the amount of chlorine supplied, (D) the supply rate, (E) the reaction temperature, and (F) the carbon dioxide concentration in the gas phase were adjusted to satisfy the conditions shown in Table 1.

The evaluation results are shown in Table 2. In the table, TMAH stands for tetramethylammonium hydroxide solution.

Example 11
<Preparation of tetramethylammonium hypochlorite solution>
As shown in FIG. 2, a reaction vessel 32 was prepared in which a polytetrafluoroethylene half joint 49 (AsOne, half female joint I type 6φ) was connected to a polytetrafluoroethylene reaction vessel (AsOne, C type cylindrical reaction vessel, 2000cc) having a capacity of 2L. 253 g of 25% by mass tetramethylammonium hydroxide aqueous solution and 747 g of ultrapure water were mixed in the reaction vessel 32 to obtain a 6.3% by mass tetramethylammonium hydroxide aqueous solution. It was confirmed that the contents of sodium, potassium, aluminum, magnesium, iron, nickel, copper, silver, cadmium, and lead contained in this tetramethylammonium hydroxide aqueous solution were each less than 1 ppb. The carbon dioxide concentration was 5 ppm (mass basis). The pH (23°C) at this time was 13.8.

A stirring rod 37 (AsOne, polytetrafluoroethylene (PTFE) stirring rod with stirring blades, total length 450 mm x diameter 8 mm) was placed in the center of the reaction vessel 32, and the top was fixed with a stirring motor 36 (Shinto Scientific, Three-One Motor BLh600). A thermometer 35 was set in the reaction vessel 32 so that the temperature during the reaction could be monitored.

The tip of a gas inlet pipe 40 (PFA tube, manufactured by Fluoron Industries Co., Ltd.) made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, which was capable of switching between chlorine gas (chlorine gas inlet pipe 39) and nitrogen gas (nitrogen gas supply pipe 41), was immersed in the bottom of the solution (tetramethylammonium hydroxide aqueous solution 33).

One half joint was connected to a chlorine gas trap 47 (gas washing bottle, manufactured by AsOne) filled with 5% by mass sodium hydroxide aqueous solution via a chlorine gas exhaust pipe 46.

The inlet side of one half joint and a magnetic pump 43 (a magnetic pump with a surface coated with Teflon (registered trademark), manufactured by AsOne) was connected with a tube made of tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA tube, manufactured by Fluoron Industries Co., Ltd.), which constitutes a reaction liquid transfer tube 42, and then the outlet side was connected with a filtration filter 44 (Fluoroguard AT, pore size 0.1 μm, manufactured by Nippon Entegris Co., Ltd.) and a reaction liquid return tube 45 made of the same material as the reaction liquid transfer tube 42.

Next, nitrogen gas with a carbon dioxide concentration of less than 1 ppm was flowed through nitrogen gas supply pipe 41 and gas supply pipe 40 (a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer tube (PFA tube, manufactured by Fluoron Industries Co., Ltd.)) at 0.29 Pa· ^m3 /sec for 20 minutes to expel carbon dioxide from the gas phase in reaction vessel 32.

Thereafter, the stirring motor 36 was rotated at 300 rpm, and while the outer periphery of the reaction vessel 32 was cooled with a reaction bath 48 (ice water), chlorine gas (commercial product; specification purity 99.999%, moisture content 0.5 ppm (mass basis) or less, carbon dioxide 1 ppm (mass basis) or less) was supplied at 0.064 Pa·m ³ /sec for 180 minutes to obtain a tetramethylammonium hypochlorite aqueous solution (total amount of chlorine gas used 6810 mL). At this time, the liquid temperature during the reaction was 11° C. In addition, when the reaction was carried out while supplying chlorine gas, the pump 43 was started, and a tetramethylammonium hypochlorite aqueous solution was produced while performing a filtration operation (the filtration operation was also carried out when the pH (23° C.) of the reaction solution became 13.5 or less).
Staff: The flow rate has been corrected.

The pH and hypochlorite ion concentration of the resulting tetramethylammonium hypochlorite aqueous solution were evaluated, and the pH was 13.0 and the hypochlorite ion concentration was 1.59 mass%. Next, the metal concentration in the tetramethylammonium hypochlorite aqueous solution was measured according to the method for measuring metal atom concentration in a quaternary alkylammonium hypochlorite solution, and the metal content was less than 1 ppb in both cases. The results are shown in Table 4.

<Examples 12 and 13>
In Examples 12 and 13, an aqueous solution of tetramethylammonium hypochlorite was produced and its metal content was examined in the same manner as in Example 11, except that the conditions shown in Table 3 were met, that is, the mass concentration of (A) the aqueous TMAH solution (wherein the contents of sodium, potassium, aluminum, magnesium, iron, nickel, copper, silver, cadmium, and lead were less than 1 ppb, and the carbon dioxide content was 2 ppm) was adjusted to meet the conditions shown in Table 3.

However, in Example 12, after all the chlorine gas was supplied, the supply of chlorine gas was stopped, and then pump 43 was started to perform the filtration operation. In Example 13, the filtration operation was not performed. The results are shown in Table 4.

<Comparative Example 11>
A tetramethylammonium hypochlorite aqueous solution was produced under the same conditions as in Example 11, except that a 1000 mL glass reaction vessel (manufactured by Shibata Scientific, 1 L separable reaction vessel) with a glass side tube having a joint size of 19/38 mm was used as the reaction vessel 32. In Comparative Example 11, filtration was performed during the production. The conditions are shown in Table 3, and the results are shown in Table 4.

<Comparative Example 12>
A 1000 mL glass three-neck flask (AsOne, three-neck glass flask) was used as the reaction vessel 32, and an aqueous solution of tetramethylammonium hypochlorite was produced under the conditions shown in Table 3. The other conditions were the same as those in Example 12. Filtration was also performed under the same conditions as in Example 12. The results are shown in Table 4.

<Comparative Example 13>
A tetramethylammonium hypochlorite aqueous solution was produced under the conditions shown in Table 3, except that a 1000 mL glass three-neck flask (AsOne, three-neck glass flask) was used as the reaction vessel 32. The other conditions were the same as in Example 13. The results are shown in Table 4.

<Example 14>
0.8 mL of 35.0 mass% high purity hydrochloric acid was added to 100 mL of the tetramethylammonium hypochlorite aqueous solution obtained in Example 11, and the pH (23°C) was adjusted to 9.6 (prepared in a PFA container). It was confirmed that the sodium, potassium, aluminum, magnesium, iron, nickel, copper, silver, cadmium, and lead contents of the obtained tetramethylammonium hypochlorite aqueous solution were each less than 1 ppb.

<Ruthenium Etching Performance Evaluation>
An oxide film was formed on a silicon wafer using a batch-type thermal oxidation furnace, and a ruthenium film was formed thereon to a thickness of 1000 Å (±10%) using a sputtering method. The sheet resistance was measured using a four-point probe resistance meter (Loresta-GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and converted into film thickness.

30 mL of the tetramethylammonium hypochlorite aqueous solution with a pH of 9.6 obtained in Example 14 was placed in a beaker (a PFA beaker), and each sample piece measuring 10 x 20 mm was immersed in the cleaning solution for 1 minute. The etching rate was calculated by dividing the change in film thickness before and after treatment by the immersion time, and the etching rate was found to be 100 Å/min or more.

<Example 21>
A tetramethylammonium hypochlorite solution was obtained in the same manner as in Example 1. The obtained aqueous solution was transferred into a glove bag in a state in which it was contained in a three-necked glass flask so as not to come into contact with the air, and after the carbon dioxide concentration in the glove bag became 1 ppm or less, it was transferred into a 1 L PFA container.

In a glove bag where the carbon dioxide concentration was 1 ppm or less, 30 mL of the obtained tetramethylammonium hypochlorite solution was poured into a PFA container, and the pH immediately after production was measured using the above-mentioned "pH measurement method," and the effective chlorine concentration immediately after production was measured using the above-mentioned "calculation method for effective chlorine concentration and hypochlorite ion concentration." The pH of the obtained tetramethylammonium hypochlorite solution was 13.0, and the effective chlorine concentration was 2.18 mass%.

<Evaluation method 2 for storage stability>
Next, the pH and available chlorine concentration of a tetramethylammonium hypochlorite solution stored for 30 days at pH 13.0 in an environment with a carbon dioxide concentration of 1 ppm or less and a storage temperature of 23°C were evaluated. The pH was 13.0 and the available chlorine concentration was 2.18 mass%, confirming that there was no change over time.

8.8 mL of 35% by mass high-purity hydrochloric acid for semiconductors (Kanto Chemical Co., Ltd., high-purity reagent Ultra Pure HCl) was added to the tetramethylammonium hypochlorite solution immediately after production and after 30 days of storage, and the solution was stirred and diluted to a pH of 9.5.

The pH of the resulting tetramethylammonium hypochlorite solution after dilution was measured and confirmed to be pH 9.5. In addition, the available chlorine concentration was measured and confirmed to be 2.18% by mass, showing no change before and after dilution.

When the etching rate of a tetramethylammonium hypochlorite solution diluted to pH 9.5 was evaluated using the above-mentioned method for calculating the etching rate of ruthenium, it was found to be 100 Å/min or more.

<Examples 22 to 27, Comparative Example 21, Reference Example>
Examples 22 to 27, Comparative Example 21, and Reference Example were adjusted and evaluated in the same manner as in Example 21, except that (A) the mass concentration of the tetramethylammonium hydroxide (TMAH) solution, (B) the pH of the TMAH solution, (F) the solution to be diluted, (G) the concentration of the solution to be diluted, and (H) the amount of the solution to be diluted were changed to the conditions shown in Table 5. However, when the pH of the tetramethylammonium hypochlorite aqueous solution after 30 days of storage was 10 or less, the tetramethylammonium hypochlorite aqueous solution was not diluted, and the etching rate was evaluated using the calculation method for the etching rate of ruthenium. The results obtained are shown in Table 6.

<Example 28>
A tetramethylammonium hypochlorite solution was obtained in the same manner as in Reference Example. The aqueous solution obtained was transferred into a glove bag in a state where it was contained in a three-neck glass flask so as not to come into contact with the air, and after the carbon dioxide concentration in the glove bag became 1 ppm or less, it was transferred into a 1 L PFA container.

In a glove bag, 100 mL of 35% by mass high-purity hydrochloric acid for semiconductors was added to 1,000 g of tetramethylammonium hypochlorite solution and stirred. The pH was measured using the above-mentioned "pH measurement method" and the effective chlorine concentration was measured using the above-mentioned "calculation method for effective chlorine concentration and hypochlorite ion concentration". The pH of the resulting tetramethylammonium hypochlorite solution was 13.0, and the effective chlorine concentration was 1.98% by mass.

Then, the pH and available chlorine concentration of a tetramethylammonium hypochlorite solution stored for 30 days at pH 13.0 in an environment with a carbon dioxide concentration of 1 ppm or less and a storage temperature of 23°C were evaluated. The pH was 13.0 and the available chlorine concentration was 1.98 mass%, confirming that there was no change over time.

8.8 mL of 35% by mass high-purity hydrochloric acid for semiconductors was added to the tetramethylammonium hypochlorite solution and stirred.

The pH of the resulting tetramethylammonium hypochlorite solution after dilution was measured and confirmed to be pH 9.5. In addition, the available chlorine concentration was measured and confirmed to be 1.98% by mass, showing no change before and after dilution.

When the etching rate of a tetramethylammonium hypochlorite solution diluted to pH 9.5 was evaluated using the above-mentioned method for calculating the etching rate of ruthenium, it was found to be 100 Å/min or more.

REFERENCE SIGNS LIST 10 Ice water 11 Three-neck flask 12 Thermometer protection tube 13 Thermocouple 14 Rotor 15 PFA tube 16 Gas washing bottle 17 5 mass% sodium hydroxide aqueous solution 18 Flowmeter 19 Water bath 21 Glass beaker 22 Thermometer protection tube 23 Thermocouple 24 Rotor 25 PFA tube 26 Flowmeter 27 Water bath 28 Ice water 31 Reaction apparatus 32 Reaction vessel 33 Quaternary alkyl ammonium hydroxide solution (before reaction)
34 Inner surface of reaction vessel 35 Thermometer 36 Stirring motor 37 Stirring rod 38 Stirring blade 39 Chlorine gas supply pipe 40 Gas inlet pipe 41 Nitrogen gas supply pipe 42 Reaction liquid transfer pipe 43 Pump 44 Filtration filter 45 Reaction liquid return pipe 46 Chlorine gas exhaust pipe 47 Chlorine gas trap 48 Reaction bath 49 Half joint

Claims (8)

A quaternary alkyl ammonium hypochlorite solution that is applied to a semiconductor wafer containing at least one selected from the group consisting of copper, tungsten, tantalum, titanium, cobalt, ruthenium, manganese, aluminum, silicon, silicon oxide, and compounds thereof, and contains less than 1 ppb of each of the metals sodium, potassium, and aluminum, and is used to remove at least one selected from the group consisting of copper, tungsten, tantalum, titanium, cobalt, ruthenium, manganese, aluminum, silicon, silicon oxide, and compounds thereof. The quaternary alkyl ammonium hypochlorite solution according to claim 1 further comprises a content of each of the metals magnesium, iron, nickel, copper, silver, cadmium, and lead of less than 1 ppb. The quaternary alkyl ammonium hypochlorite solution according to claim 1 or 2, wherein the quaternary alkyl ammonium hypochlorite is tetramethyl ammonium hypochlorite. A method for producing a quaternary alkyl ammonium hypochlorite solution, comprising the steps of:
The method includes the steps of: preparing a quaternary alkyl ammonium hydroxide solution; and contacting the quaternary alkyl ammonium hydroxide solution with chlorine.
The pH of the liquid phase in the reaction step is 10.5 or more and less than 14.
A method for producing a quaternary alkyl ammonium hypochlorite solution. The method according to claim 4, wherein the quaternary alkyl ammonium hydroxide solution prepared in the preparation step is a solution of quaternary alkyl ammonium hydroxide having an alkyl group with 1 to 10 carbon atoms. The method according to claim 4 or 5, wherein the reaction temperature in the reaction step is -35°C or higher and 15°C or lower. The method according to any one of claims 4 to 6, further comprising a step of filtering the quaternary alkyl ammonium hypochlorite solution obtained in the reaction step. The method according to claim 7, wherein the pH of the quaternary alkyl ammonium hypochlorite solution to be filtered at 25°C is 13.5 or less.

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